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JSR 354 provides an API for representing, transporting, and performing comprehensive calculations with Money and Currency. This module implements JSR 354.

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/*
  Copyright (c) 2012, 2014, Credit Suisse (Anatole Tresch), Werner Keil and others by the @author tag.

  Licensed under the Apache License, Version 2.0 (the "License"); you may not
  use this file except in compliance with the License. You may obtain a copy of
  the License at

  http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  License for the specific language governing permissions and limitations under
  the License.
 */
package org.javamoney.moneta.function;

import static java.text.NumberFormat.getPercentInstance;

import java.math.BigDecimal;
import java.math.MathContext;
import java.util.Objects;

import javax.money.MonetaryAmount;
import javax.money.MonetaryOperator;

/**
 * This class allows to extract the percentage of a {@link MonetaryAmount}
 * instance.
 *
 * @version 0.5
 * @author Werner Keil
 *
 * @see Wikipedia: Percentage
 */
final class PercentOperator implements MonetaryOperator {

	private static final BigDecimal ONE_HUNDRED = new BigDecimal(100,
			MathContext.DECIMAL64);

	private final BigDecimal percentValue;

	/**
	 * Access the shared instance of {@link PercentOperator} for use.
	 */
	PercentOperator(final BigDecimal decimal) {
		percentValue = calcPercent(decimal);
	}

	/**
	 * Gets the percentage of the amount.
	 *
	 * This returns the monetary amount in percent. For example, for 10% 'EUR
	 * 2.35' will return 0.235.
	 *
	 * This is returned as a {@code MonetaryAmount}.
	 *
	 * @return the percent result of the amount, never {@code null}
	 */
	@Override
	public MonetaryAmount apply(MonetaryAmount amount) {
		Objects.requireNonNull(amount, "Amount required.");
		return amount.multiply(percentValue);
	}

	/*
	 * (non-Javadoc)
	 *
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString() {
		return getPercentInstance().format(percentValue);
	}

	/**
	 * Calculate a BigDecimal value for a Percent e.g. "3" (3 percent) will
	 * generate .03
	 *
	 * @return java.math.BigDecimal
	 * @param decimal
	 *            java.math.BigDecimal
	 */
	private static BigDecimal calcPercent(BigDecimal decimal) {
		return decimal.divide(ONE_HUNDRED, MathContext.DECIMAL64); // we now
																	// have
	}

}